I think this (http://blogs.msdn.com/oldnewthing/archive/2006/08/14/699521.aspx or http://www.dailycupoftech.com/2007/03/11/mia-ram-in-32-bit-vista/ describes it) is the problem.
There are definitely 4 1GB sticks of RAM in my machine, so I doubt it’s hardware. Plus, when I boot the computer, the BIOS sees the full 4 GB. So it’s some dumb Windows limitation and if I override it by “enabling PAE” then I could run into all sorts of problems. It probably isn’t worth it.
Anyone been through this experience with Vista and RAM limitations?